1. Field of the Invention
The present invention relates to a method for fabricating color filter substrates.
2. Description of the Prior Art
Thin film transistor liquid crystal displays (TFT-LCDs) primarily utilize thin film transistors arranged in the form of a matrix, capacitors, and electronic devices such as conversion pads to drive liquid crystal pixels for producing vivid color pictures. Since TFT-LCDs have the advantage of portability, low power consumption, and low radiation, they have been widely used in various portable electronic products, such as notebook computers and personal digital assistants (PDAs). The TFT-LCDs are also gradually replacing the cathode ray tube (CRT) monitors used with conventional desktop computers.
In general, TFT-LCDs include a TFT substrate having a plurality of thin film transistors arranged in a matrix, pixel electrodes, a plurality of scan lines or data lines arranged orthogonally, a color filter substrate having a plurality of color filters arranged in a matrix, and a liquid crystal layer disposed between the TFT substrate and the color filter substrate. Preferably, a plurality of deposition and photo-etching-processes (PEP) are performed to fabricate the thin film transistors on the surface of the TFT substrate, and a plurality of photolithography processes are performed to form the color filters on the color filter substrate, thereby providing the vivid color for each pixel of the TFT-LCD.
Please refer to FIG. 1 to FIG. 6. FIG. 1 to FIG. 6 are perspective diagrams showing the means of fabricating a color filter substrate according to the prior art. As shown in FIG. 1, a substrate 12, such as a glass substrate is first provided. An inorganic film 14 composed of chromium and a light sensitive film 16 composed of polyimide are disposed on the surface of the substrate 12 thereafter. Next, as shown in FIG. 2, a patterning process is performed by utilizing a mask to perform an exposure and development process on the light sensitive film 16 to define a plurality of banks 18 and openings 20.
As shown in FIG. 3, an etching process is performed on the inorganic film 14 to remove the region not covered by the patterned light sensitive film 16 and further form the plurality of banks 18 and the openings 20 by utilizing the light sensitive film 16 as a hardmask. A surface treatment is performed thereafter on the surface of the substrate 12, the openings 20, and the banks 18. Since a higher chemical affinity is found between the banks 18 and the color filter formed afterwards, the banks 18 will exhibit a hydrophobic characteristic. The surface of the substrate 12 within openings 20 on the other hand, exhibits a hydrophilic characteristic as a lower chemical affinity is measured between the substrate 12 and the color filter.
As shown in FIG. 4, an ink jet process is performed to utilize a print head 22 to dispose a color filter material 24 into each of the openings 20, in which the color filter material 24 includes red ink, green ink, and blue ink. Next, as shown in FIG. 5, a coating process is performed to form a passivation layer 26 on the color filter material 24 and the banks 18 and to planarize the surface of the substrate 12. Subsequently, as shown in FIG. 6, a transparent conductive layer 28 composed of indium tin oxide (ITO) or indium zinc oxide (IZO) is formed on the passivation layer 26 to complete the process of fabricating a color filter substrate.
However, due to strong variation between the chemical affinity of the materials, the color filter material disposed on the surface of the substrate 12 often produce an uneven surface or poor overall shape. In order to solve this problem, the conventional technique generally disposes a passivation layer over the surface of the color filter material to planarize the surface of the color filter material, such as the structure shown in FIG. 5. However, despite the fact that the structure may reduce the problem of uneven color filter surface, other side effects such as poor light transmittance and light usage will result.